Pyridine derivatives have, for many years, been investigated for use in the biological sciences. Pyridine dicarboxylate compounds useful as herbicides are described in U.S. Pat. No. 4,692,184. These compounds have fluorinated methyl groups at the 2- and 6-positions and carboxylic acids or their derivatives at the 3- and 5-positions and are characterized further by a 4-position substituent in which the atom attached to the pyridine ring is a carbon atom, such as alkyl, alkoxyalkyl, alkylthioalkyl, aralkyl, and like moieties.
More relevant compounds include those which contain fluorinated methyl groups at the 2- and 6-positions, carboxylic acids or their derivatives at the 3- and/or 5-positions and at the 4-position have a substituent group beginning with a hetero atom selected from O, S, N and P. These compounds are likewise useful as herbicides.
Other herbicidal pyridines are those of U.S. Pat. No. 4,609,399 which have a fluorinated methyl group at the 2-position, a carboxylic acid group or derivative thereof at the 3- and/or 5-position, and alkoxy groups at the 4- and 6-positions.
More relevant to the compounds of this invention are those disclosed in U.S. Pat. No. 4,885,026, which are 5-amino pyridine 3-carboxylate derivatives.